1. Field
The present invention generally relates to a hologram generation apparatus and method and particularly, to a phase-regularized polygon hologram generation apparatus and method for holographic 3D display.
2. Description of Related Art
At present, research is being actively made for three-dimensional (3D) imaging and image generating techniques. 3D imaging and related media is realistic imaging media of a new concept, which brings the standard of visual information to a higher dimension, and the imaging media is expected to lead next-generation imaging devices. While currently existing 2D imaging systems provide planar imaging, 3D imaging systems utilize and may thus offer the ultimate image-generating technique in that 3D imaging systems provide actual/true imaging information to user-observers.
Currently being researched and developed are 3D imaging techniques, including stereoscopy, holography, and integral imaging. Of these, holography technique enables a 3D image to be made, without eyeglasses for viewing, by reconstructing a hologram formed by using a laser.
Holography technique uses a principle of recording and reconstructing interference signals obtained when light reflected from an object (object beam) and light with coherency (reference beam) intersect with each other. Using a laser beam with high coherency, a hologram is made by recording on a photographic film, interference patterns created by intersecting and interfering of the object beam, which is directed at the object and scattered off from the object, and a reference beam, which is directed from another direction. When the object beam and the reference beam intersect, interference patterns are formed, and the interference patterns are recorded with amplitude and phase information. The interference patterns include intensity and phase information of light waves. Intensity information is recorded as contrast between patterns in the interference patterns, and amplitude information is recorded as a distance between patterns in the interference patterns. Directing a reference light at thus recorded interference patterns and reconstructing the interference patterns recorded in the hologram as a 3D image is called holography.
A computer-generated hologram (CGH), which uses a computer for storing, transmitting, and imaging of hologram patterns, has also been developed. CGHs have been developed in various ways, and recently, with advances in the digital industry, systems have been developed to take CGHs beyond a still-image stage to a video/display realm.
By using a computer, a CGH system may compute an interference pattern and generate an hologram interference pattern image. A CGH system transmits data for the hologram interference pattern image to a spatial light modulator (SLM). When a reference light is directed at the SLM, the hologram interference pattern displayed on the SLM is reconstructed as a 3D image.
FIG. 1 shows components of a digital hologram generation apparatus implementing computer-generated hologram (CGH) method according to a conventional technology. Referring to FIG. 1, a computer (10) generates hologram interference pattern data applicable to a 3D image to be obtained. The hologram interference pattern generated is transmitted to a spatial light modulator (SLM) (20). The SLM (20) may be built as a backlit liquid crystal display (LCD) panel and display the hologram interference pattern thereon. At one side of the SLM (20), there is a laser light source (30) to be used to emit a reference light. To evenly distribute the reference light (90) emitted from the laser light source (30) on front side of the SLM (20), an expander (40) and a lens (50) may be positioned in a sequential order. The reference light (90) from the laser light source (30) passes through the expander (40) and the lens (50) and is directed to a side of the SLM (20). Where the SLM (20) is a backlit LCD panel, a 3D image (80), which is formed by the hologram interference pattern displayed on the SLM (20), is displayed on another side of the SLM (20). A field lens is denoted by FL.
For displaying a holographic image, a CGH is formed, and hologram interference pattern data is created using the CGH, based on point cloud or polygon modeling technique. Point cloud CGH technique may be used for representing a 3D object as a set of data points, and polygon CGH technique may be used for representing a 3D object as a set of polygonal facets. As the point cloud CGH technique requires a large amount of data for detailed representation, the polygon CGH technique is used more often for 3D object modeling.
However, when the polygon CGH is used, there exist dark line defects, which are observed in the holographic 3D image at or between triangles.
FIG. 2 shows a cause of the dark line defects in a polygon computer generated hologram (polygon CGH).
As shown in FIG. 2, an abrupt change is observed in the wavefront created between the triangles when a plane wave is incident on a triangular aperture. As a result, diffraction of the incident plane wave occurs, and some high order components move beyond the eye lens region of an observer and energy decreases. When actually observed by the observer, these are recognized as dark-line defects.
FIG. 3 shows a holographic 3D image with actual dark-line defects.
Conventional polygon CGH continues to have the dark-line defects, and holographic images obtained from the conventional polygon CGH still lacks clarity thereby posing a problem.